Commit Graph

4878 Commits

Author SHA1 Message Date
Douglas Yung c5109d3c79 Fix path in test added in e0577b3130 to work with both Linux/Windows paths.
Patch by Ying Yi!
2021-03-30 04:17:29 -07:00
Markus Böck 142d522ded [llvm-profdata] Make sure to consume Error on the error path of setIsIRLevelProfile
Encountered a crash while running a debug build, where this code path would be taken due to a mismatch in profile coverage data versions. Without consuming the error, an assert would be triggered inside the destructor of Error.

Differential Revision: https://reviews.llvm.org/D99457
2021-03-30 08:52:58 +02:00
Jonas Devlieghere b19a9efbc9 [dsymutil] s/dwarfdump/llvm-dwarfdump/ in test 2021-03-29 17:14:35 -07:00
Jonas Devlieghere e0577b3130 [dsymutil] Relocate DW_TAG_label
dsymutil is not relocating the DW_AT_low_pc for a DW_TAG_label. This
patch fixes that and adds a test.

Differential revision: https://reviews.llvm.org/D99534
2021-03-29 15:45:48 -07:00
Wenlei He 30b0232336 [CSSPGO][llvm-profgen] Context-sensitive global pre-inliner
This change sets up a framework in llvm-profgen to estimate inline decision and adjust context-sensitive profile based on that. We call it a global pre-inliner in llvm-profgen.

It will serve two purposes:
  1) Since context profile for not inlined context will be merged into base profile, if we estimate a context will not be inlined, we can merge the context profile in the output to save profile size.
  2) For thinLTO, when a context involving functions from different modules is not inined, we can't merge functions profiles across modules, leading to suboptimal post-inline count quality. By estimating some inline decisions, we would be able to adjust/merge context profiles beforehand as a mitigation.

Compiler inline heuristic uses inline cost which is not available in llvm-profgen. But since inline cost is closely related to size, we could get an estimate through function size from debug info. Because the size we have in llvm-profgen is the final size, it could also be more accurate than the inline cost estimation in the compiler.

This change only has the framework, with a few TODOs left for follow up patches for a complete implementation:
  1) We need to retrieve size for funciton//inlinee from debug info for inlining estimation. Currently we use number of samples in a profile as place holder for size estimation.
  2) Currently the thresholds are using the values used by sample loader inliner. But they need to be tuned since the size here is fully optimized machine code size, instead of inline cost based on not yet fully optimized IR.

Differential Revision: https://reviews.llvm.org/D99146
2021-03-29 09:46:14 -07:00
Andrew Savonichev bba25a9cd8 [MCA] Support carry-over instructions for in-order processors
Instructions that have more uops than the processor's IssueWidth are
issued in multiple cycles.

The patch fixes PR49712.

Differential Revision: https://reviews.llvm.org/D99339
2021-03-26 00:06:19 +03:00
Konstantin Zhuravlyov f4ace63737 AMDGPU: Add target id and code object v4 support
- Add target id support (https://clang.llvm.org/docs/ClangOffloadBundler.html#target-id)
  - Add code object v4 support (https://llvm.org/docs/AMDGPUUsage.html#elf-code-object)
    - Add kernarg_size to kernel descriptor
    - Change trap handler ABI to no longer move queue pointer into s[0:1]
  - Cleanup ELF definitions
    - Add V2, V3, V4 suffixes to make a clear distinction for code object version
    - Consolidate note names

Differential Revision: https://reviews.llvm.org/D95638
2021-03-24 11:54:05 -04:00
Vinicius Tinti 804ff7f293 [llvm-objdump] Implement --prefix-strip option
The option `--prefix-strip` is only used when `--prefix` is not empty.
It removes N initial directories from absolute paths before adding the
prefix.

This matches GNU's objdump behavior.

Reviewed By: jhenderson

Differential Revision: https://reviews.llvm.org/D96679
2021-03-24 13:22:35 +00:00
Andrew Savonichev 292da93d59 [MCA] Disable RCU for InOrderIssueStage
This is a follow-up for:
D98604 [MCA] Ensure that writes occur in-order

When instructions are aligned by the order of writes, they retire
in-order naturally. There is no need for an RCU, so it is disabled.

Differential Revision: https://reviews.llvm.org/D98628
2021-03-24 13:54:04 +03:00
Andy Wingo 9ac5620cb8 [WebAssembly] Rename WasmLimits::Initial to ::Minimum. NFC.
This patch renames the "Initial" member of WasmLimits to the name used
in the spec, "Minimum".

In the core WebAssembly specification, the Limits data type has one
required "min" member and one optional "max" member, indicating the
minimum required size of the corresponding table or memory, and the
maximum size, if any.

Although the WebAssembly spec does instantiate locally-defined tables
and memories with the initial size being equal to the minimum size, it
can't impose such a requirement for imports.  It doesn't make sense to
require an initial size for a memory import, for example.  The compiler
can only sensibly express the minimum and maximum sizes.

See
https://github.com/WebAssembly/js-types/blob/master/proposals/js-types/Overview.md#naming-of-size-limits
for a related discussion that agrees that the right name of "initial" is
"minimum" when querying the type of a table or memory from JavaScript.
(Of course it still makes sense for JS to speak in terms of an initial
size when it explicitly instantiates memories and tables.)

Differential Revision: https://reviews.llvm.org/D99186
2021-03-24 09:10:11 +01:00
Jay Foad fc7e3e7dd9 [AMDGPU] Set SchedRW on real instructions
Coyp SchedRW from pseudos to real instructions so that llvm-mca has
access to it. This is NFC for normal compiler codegen, which schedules
pseudos not real instructions.

Add an llvm-mca test for some high latency double-precision instructions
as a smoke test.

Differential Revision: https://reviews.llvm.org/D99187
2021-03-23 15:38:11 +00:00
Andrea Di Biagio f5bdc88e4d [MCA] Improved handling of negative read-advance cycles.
Before this patch, register writes were always invalidated by the
RegisterFile at instruction commit stage. So,
the RegisterFile was often losing the knowledge about the `execute
cycle` of writes already committed. While this was not problematic
for non-delayed reads, this was sometimes leading to inaccurate read
latency computations in the presence of negative read-advance cycles.

This patch fixes the issue by changing how the RegisterFile component
internally keeps track of the `execute cycle` information of each
write. On every instruction executed, the RegisterFile gets notified
by the RetireStage, so that it can internally record the execute
cycle of each executed write.
The `execute cycle` information is stored within WriteRef itself, and
it is not invalidated when the write is committed.
2021-03-23 14:47:23 +00:00
Yvan Roux 241032a205 [llvm-symbolizer][llvm-nm] Fix AArch64 and ARM mapping symbols handling.
Exclude AArch64 mapping symbols ($x and $d) for symtab symbolization as
it was done for ARM since D95916 tom bring bots back to green state.

This is implemented by setting SF_FormatSpecific such that
llvm-symbolizer will ignore them, and use this flag to re-implement
llvm-nm --special-syms option which make it work for both targets.

Differential Revision: https://reviews.llvm.org/D98803
2021-03-23 14:17:12 +01:00
Rahman Lavaee 949abf7d6a [llvm-readelf, propeller] Add fallthrough bit to basic block metadata in BB-Address-Map section.
This patch adds a fallthrough bit to basic block metadata, indicating whether the basic block can fallthrough without taking any branches. The bit will help us avoid an intel LBR bug which results in occasional duplicate entries at the beginning of the LBR stack.

This patch uses `MachineBasicBlock::canFallThrough()` to set the bit. This is not a const method because it eventually calls `TargetInstrInfo::analyzeBranch`, but it calls this function with the default `AllowModify=false`. So we can either make the argument to the `getBBAddrMapMetadata` non-const, or we can use `const_cast` when calling `canFallThrough`. I decide to go with the latter since this is purely due to legacy code, and in general we should not allow the BasicBlock to be mutable during `getBBAddrMapMetadata`.

Reviewed By: tmsriram

Differential Revision: https://reviews.llvm.org/D96918
2021-03-22 21:38:05 -07:00
Jonas Devlieghere 3d6c7d6e8e [dsymutil] Fix spurious warnings for missing symbols with thinLTO
Fix spurious warnings for missing symbols with thinLTO. The latter
appends a unique suffix to avoid collisions for exported private
symbols, resulting in dsymutil complaining it couldn't find the symbol
in the object file.

rdar://75434058

Differential revision: https://reviews.llvm.org/D99125
2021-03-22 18:36:39 -07:00
Wenlei He ce6bfe9411 [CSSPGO][llvm-profgen] Use profile summary based threshold for context trimming and merging
Switch to use cold threshold from profile summary for cold context merging and trimming, instead of relying on hard coded values. Minor refactoring included for switch names, etc.

Differential Revision: https://reviews.llvm.org/D98921
2021-03-22 08:56:59 -07:00
Andrew Litteken 0776eca7a4 Revert "[IRSim] Adding basic implementation of llvm-sim."
Causing build errors on the Windows Buildbots.

This reverts commit 5155dff278.
2021-03-20 18:03:09 -05:00
Andrew Litteken 5155dff278 [IRSim] Adding basic implementation of llvm-sim.
This is a similarity visualization tool that accepts a Module and
passes it to the IRSimilarityIdentifier.  The resulting SimilarityGroups
are output in a JSON file.

Tests are found in test/tools/llvm-sim and check for the file not found,
a bad module, and that the JSON is created correctly.

Reviewers: paquette, jroelofs, MaskRay

Recommit of: 15645d044b to fix linking
errors.

Differential Revision: https://reviews.llvm.org/D86974
2021-03-20 16:47:50 -05:00
Fangrui Song 948be862d6 [llvm-readobj] Remove legacy GNU_PROPERTY_X86_ISA_1_{NEEDED,USED} and dump new GNU_PROPERTY_X86_ISA_1_{NEEDED,USED}
https://sourceware.org/bugzilla/show_bug.cgi?id=26703 deprecated the
previous GNU_PROPERTY_X86_ISA_1_{CMOV,SSE,*} values (renamed to `COMPAT`)
and added new values.

Since the legacy values are not used by compilers, having dumping support in
llvm-readobj is unnecessary. So just drop the legacy feature.

The new values are used by GCC 11
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97250) `-march=x86-64-v[234]` to
indicate the micro-architecture ISA levels.

Differential Revision: https://reviews.llvm.org/D98818
2021-03-19 14:35:22 -07:00
Wenlei He 1410db70b9 [CSSPGO] Add attribute metadata for context profile
This changes adds attribute field for metadata of context profile. Currently we have an inline attribute that indicates whether the leaf frame corresponding to a context profile was inlined in previous build.

This will be used to help estimating inlining and be taken into account when trimming context. Changes for that in llvm-profgen will follow. It will also help tuning.

Differential Revision: https://reviews.llvm.org/D98823
2021-03-18 22:00:56 -07:00
Andrew Savonichev e6ce0db378 [MCA] Ensure that writes occur in-order
Delay the issue of a new instruction if that leads to out-of-order
commits of writes.

This patch fixes the problem described in:
https://bugs.llvm.org/show_bug.cgi?id=41796#c3

Differential Revision: https://reviews.llvm.org/D98604
2021-03-18 17:10:20 +03:00
Chen Zheng 12824266c7 [NFC] make XCOFF dwarf dump test run only on PowerPC target. 2021-03-17 21:59:47 -04:00
Chen Zheng d33b016ada [XCOFF][llvm-dwarfdump] llvm-dwarfdump support for XCOFF
Author: hubert.reinterpretcast, shchenz

Reviewed By: jasonliu, echristo

Differential Revision: https://reviews.llvm.org/D97186
2021-03-17 21:21:51 -04:00
Eric Astor 1236dbc2fa [ms] [llvm-ml] Allow the /Zs parameter as a synonym for -filetype=null
For ml.exe, /Zs implies a syntax check with no output files.

Reviewed By: thakis

Differential Revision: https://reviews.llvm.org/D90061
2021-03-17 12:18:43 -04:00
Fangrui Song 8fbedb6b90 [llvm-nm] Add --format=just-symbols and make --just-symbol-name its alias
https://sourceware.org/bugzilla/show_bug.cgi?id=27487 binutils will have
--format=just-symbols/-j as well.

Arbitrarily prefer `-j` to `--format=sysv`. Previously `--format=sysv -j` prints
in the sysv format while `-j` takes precedence over other formats.

Differential Revision: https://reviews.llvm.org/D98569
2021-03-16 10:07:01 -07:00
David Zarzycki 0fda5e8441 [llvm-exegesis testing] Workaround unreliable test
Picking an instruction at random is not perfectly reliable.
2021-03-16 08:00:14 -04:00
wlei dddd590fd0 [CSSPGO][llvm-profgen] Fix getCanonicalFnName usage in llvm-profgen
Previously we didn't support to keep the unique linkage name(-funique-internal-linkage-name) in llvm-profgen. As discussed in https://reviews.llvm.org/D96932, we choose to do canonicalization for it.

Now since "selected" is set as the default parameter of getCanonicalFnName in `D96932`, we don't need to add any attribute here for the previous usage and only fix the missing usage in the pseudo probe decoding.

Differential Revision: https://reviews.llvm.org/D98226
2021-03-15 21:00:42 -07:00
Wael Yehia c05990a0cc [PATCH] fix location of test case
from D97507.
2021-03-15 09:34:24 -04:00
Johannes Doerfert cd1bd6e587 [Utils] Check for more global information in update_test_checks
This allows to check for various globals (metadata/attributes/...) and
also resolves problems with globals (metadata/attributes/...) being
reused across different prefixes.

Reviewed By: sstefan1

Differential Revision: https://reviews.llvm.org/D94741
2021-03-11 23:31:16 -06:00
David Blaikie 7906c0309b Move (llvm-original-di-preservation) test example output into the Inputs directory (since it's an input to the test execution)
The "Inputs" subdirectory is used for all files read by the test, not
only those used as input to the execution - so even though this file is
used as a golden reference for the output of the test, it's still an
input to the test execution (it is read in the process of executing the
test).
2021-03-11 17:36:33 -08:00
Jay Foad 7340fd6886 [MCA] Support in-order CPUs with MicroOpBufferSize=1
Differential Revision: https://reviews.llvm.org/D98356
2021-03-11 10:12:54 +00:00
Djordje Todorovic 9f41c03f82 [Debugify][OriginalDIMode] Export the report into JSON file
By using the original-di check with debugify in the combination with
the llvm/utils/llvm-original-di-preservation.py it becomes very user
friendly tool. An example of the HTML page with the issues
related to debug info can be found at [0].

[0] https://djolertrk.github.io/di-checker-html-report-example/

Differential Revision: https://reviews.llvm.org/D82546
2021-03-11 01:11:13 -08:00
Zequan Wu 8d5c3ae357 Revert "[llvm-cov] reset executation count to 0 after wrapped segment"
This reverts D85036

Differential Revision: https://reviews.llvm.org/D98084
2021-03-09 14:47:32 -08:00
Alexander Shaposhnikov ede56e5127 [llvm-objcopy][MachO] Add support for --keep-undefined
This diff introduces --keep-undefined in llvm-objcopy/llvm-strip for Mach-O
which makes the tools preserve undefined symbols.

Test plan: make check-all

Differential revision: https://reviews.llvm.org/D97040
2021-03-08 18:57:25 -08:00
Alexander Shaposhnikov 5f2f84a68a [llvm-objdump][MachO] Add support for dumping function starts
Add support for dumping function starts for Mach-O binaries.

Test plan: make check-all

Differential revision: https://reviews.llvm.org/D97027
2021-03-08 18:44:44 -08:00
Rahman Lavaee c245c21c43 [llvm-readelf] Support dumping the BB address map section with --bb-addr-map.
This patch lets llvm-readelf dump the content of the BB address map
section in the following format:
```
Function {
  At: <address>
  BB entries [
    {
      Offset:   <offset>
      Size:     <size>
      Metadata: <metadata>
    },
    ...
  ]
}
...
```

Reviewed By: jhenderson

Differential Revision: https://reviews.llvm.org/D95511
2021-03-08 16:20:11 -08:00
wlei c460ef61d6 [CSSPGO][llvm-profgen] Change sample count of dangling probe in llvm-profgen
Differential Revision: https://reviews.llvm.org/D96811
2021-03-08 14:36:02 -08:00
Hongtao Yu e68fafa49f [CSSPGO] llvm-profdata support for CS profile.
Context-sensitive AutoFDO profile has a different name scheme where full calling contexts are encoded as function names. When processing CS proifle, llvm-profdata should use full contexts instead of leaf function names.

Reviewed By: wmi, wenlei, wlei

Differential Revision: https://reviews.llvm.org/D97998
2021-03-08 09:04:40 -08:00
Keith Smiley 64240f8138 llvm-nm: add flag to suppress no symbols warning
This spelling matches binutils https://sourceware.org/bugzilla/show_bug.cgi?id=27408

Differential Revision: https://reviews.llvm.org/D83152
2021-03-07 16:20:13 -08:00
Abhina Sreeskantharajan c52fe0b021 [test] Use host platform specific error message substitution in lit tests
This patch uses the errno python library to print out the correct error messages instead of hardcoding the error message per platform.

Reviewed By: jhenderson, ASDenysPetrov

Differential Revision: https://reviews.llvm.org/D97472
2021-03-05 07:21:53 -05:00
James Henderson 076698154a [llvm-objcopy] Fix crash for binary input files with non-ascii names
The code was using the standard isalnum function which doesn't handle
values outside the non-ascii range. Switching to using llvm::isAlnum
instead ensures we don't provoke undefined behaviour, which can in some
cases result in crashes.

Reviewed by: MaskRay

Differential Revision: https://reviews.llvm.org/D97663
2021-03-05 08:57:40 +00:00
James Henderson 47c343d768 [llvm-objcopy][test] Fix test that could have passed spuriously
The test was showing that when --strip-unneeded is specified for an
executable, all the symbols are stripped. However, the set of symbols
used in the test would be stripped by --strip-unneeded for an ET_REL
object too. Fix this by adding additional symbols that aren't normally
stripped by --strip-unneeded.

Reviewed by: MaskRay

Differential Revision: https://reviews.llvm.org/D97664
2021-03-05 08:57:39 +00:00
Haowei Wu db06088d63 [llvm-ifs] Add option to use InterfaceStub library
This change adds '-use-interfacestub' option to allow llvm-ifs
to use InterfaceStub lib when generating ELF binary.

Differential Revision: https://reviews.llvm.org/D94461
2021-03-04 11:28:49 -08:00
James Henderson 1562e4552c [llvm-objcopy][llvm-strip][test] Improve testing
This patch adds a number of new test cases that cover various
llvm-objcopy and llvm-strip features that had missing test coverage of
various descriptions:
* --add-section - checked the shdr properties, not just the content.
* Dedicated test case for --add-symbol when there are many sections.
* Show that --change-start accepts negative values without overflow.
  This was previously present but got lost between review versions.
* --dump-section - show that multiple sections can be dumped
  simultaneously to different files, and that an error is reported when
  a section cannot be found.
* --globalize-symbol(s) - show that symbols that are not mentioned are
  not globalized, if they would otherwise be, and that missing symbols
  from the list do not cause problems.
* --keep-global-symbol - show that the --regex option can be used in
  conjunction with this option.
* --keep-symbol - show that the --regex option can be used in
  conjunction with this option.
* --localize-symbol(s) - show that symbols that are not mentioned are
  not localized, if they would otherwise be, and that missing symbols
  from the list do not cause problems.
* --prefix-alloc-sections - show the behaviour of an empty string
  argument and multiple arguments.
* --prefix-symbols - show the behaviour of an empty string argument and
  multiple arguments. Also show the option applies to undefined symbols.
* --redefine-symbol - show that symbols with no name can be renamed,
  that it is not an error if a symbol is not specified, and that the
  option doesn't chain (i.e. --redefine-sym a=b --redefine-sym b=c does
  not redefine a as c).
* --rename-section - show that all section flags are preserved if none
  are specified. Also show that the option does not chain.
* --set-section-alignment - show that only specified sections have
  their alignments changed.
* --set-section-flags - show which section flags are preserved when this
  option is used. Also show that unspecified sections are not affected.
* --preserve-dates - show that -p is an alias of --preserve-dates.
* --strip-symbol - show that --regex works with this option for
  llvm-objcopy as well as llvm-strip.
* --strip-unneeded-symbol(s) - show more clearly that needed symbols are
  not stripped even if requested by this option.
* --allow-broken-links - show the sh_link of a symbol table is set to 0
  when its string table has been removed when this option is specified.
* --weaken-symbol(s) - show that symbols that are not mentioned are not
  weakened, if they would otherwise be, and that missing symbols from
  the list do not cause problems.
* --wildcard - show the wildcard behaviour for several options that were
  previously unchecked.

Reviewed by: alexshap

Differential Revision: https://reviews.llvm.org/D97666
2021-03-04 11:32:27 +00:00
Oliver Stannard aac056c528 [objdump][ARM] Use correct offset when printing ARM/Thumb branch targets
llvm-objdump only uses one MCInstrAnalysis object, so if ARM and Thumb
code is mixed in one object, or if an object is disassembled without
explicitly setting the triple to match the ISA used, then branch and
call targets will be printed incorrectly.

This could be fixed by creating two MCInstrAnalysis objects in
llvm-objdump, like we currently do for SubtargetInfo. However, I don't
think there's any reason we need two separate sub-classes of
MCInstrAnalysis, so instead these can be merged into one, and the ISA
determined by checking the opcode of the instruction.

Differential revision: https://reviews.llvm.org/D97766
2021-03-04 11:15:57 +00:00
Andrew Savonichev d791695cb5 [MCA] Add support for in-order CPUs
This patch adds a pipeline to support in-order CPUs such as ARM
Cortex-A55.

In-order pipeline implements a simplified version of Dispatch,
Scheduler and Execute stages as a single stage. Entry and Retire
stages are common for both in-order and out-of-order pipelines.

Differential Revision: https://reviews.llvm.org/D94928
2021-03-04 14:08:19 +03:00
James Henderson 8bb74d16ef [llvm-objcopy/strip] Fix off-by-one error in SYMTAB_SHNDX need check
The check for whether an extended symbol index table was required
dropped the first SHN_LORESERVE sections from the sections array before
checking whether the remaining sections had symbols. Unfortunately, the
null section header is not present in this list, so the check was
skipping the first section that might be important. If that section
contained a symbol, and no subsequent ones did, the .symtab_shndx
section would not be emitted, leading to a corrupt object.

Also consolidate and expand test coverage in the area to cover this bug
and other aspects of the SYMTAB_SHNDX section.

Reviewed by: alexshap, MaskRay

Differential Revision: https://reviews.llvm.org/D97661
2021-03-04 10:23:45 +00:00
James Henderson 49c91a64fd [llvm-objcopy][test] Improve many-sections object and test case
Additionally do some test tidy-ups and improve coverage of symbol
section indexes where the logical section index >= SHN_LORESERVE.

The symbol and section names in the many-section input object were
mostly shared. This patch changes them to be distinct, enabling
different operations such as --add-symbol, to be more targeted, when
using the object. It also makes the test less confusing and removes some
oddness in the symbol table order, presumably caused by the duplicate
names.

The input object was built from assembly that was of the form:
.section s1
sym1:
.section s2
sym2:
...
with a total of 65536 such occurrences. llvm-objcopy was then used to
remove the empty .text section automatically generated by MC, and
incidentally to move .strtab to the end of the object. This ensured that
the section/symbol indexes matched their name (i.e. section index 1 was
s1, section index 2 was s2 etc, and sym1 was in s1, sym2 in s2 etc).

Reviewed by: MaskRay

Differential Revision: https://reviews.llvm.org/D97660
2021-03-04 09:42:43 +00:00
Hongtao Yu ad2a59f584 [CSSPGO] Introducing dangling pseudo probes.
Dangling probes are the probes associated to an empty block. This usually happens when all real instructions are optimized away from the block. There is a problem with dangling probes during the offline counts processing. The way the sample profiler works is that samples collected on the first physical instruction following a probe will be counted towards the probe. This logically equals to treating the instruction next to a probe as if it is from the same block of the probe. In the dangling probe case, the real instruction following a dangling probe actually starts a new block, and samples collected on the new block may cause issues when counted towards the empty block.

To mitigate this issue, we first try to move around a dangling probe inside its owning block. If there are still native instructions preceding the probe in the same block, we can then use them as a place holder to collect samples for the probe. A pass is added to walk each block backwards looking for probes not followed by any real instruction and moving them before the first real instruction. This is done right before the object emission.

If we are unlucky to find such in-block preceding instructions for a probe, the solution we are taking is to tag such probe as dangling so that the samples reported for them will not be trusted by the compiler. We leave it up to the counts inference algorithm to get such probes a reasonable count. The number `UINT64_MAX` is used to mark sample count as collected for a dangling probe.

Reviewed By: wmi

Differential Revision: https://reviews.llvm.org/D95962
2021-03-03 22:44:41 -08:00
Fangrui Song 584cb67d2d [IRSymTab] Set FB_used on llvm.compiler.used symbols
IR symbol table does not parse inline asm. A symbol only referenced by inline
asm is not in the IR symbol table, so LTO does not know that the definition (in
another translation unit) is referenced and may internalize it, even if that
definition has `__attribute__((used))` (which lowers to `llvm.compiler.used` on
ELF targets since D97446).

```
// cabac.c
__attribute__((used)) const uint8_t ff_h264_cabac_tables[...] = {...};

// h264_cabac.c
  asm("lea ff_h264_cabac_tables(%rip), %0" : ...);
```

`__attribute__((used))` is the recommended way to tell the compiler there may
be inline asm references, so the usage is perfectly fine. This patch
conservatively sets the `FB_used` bit on `llvm.compiler.used` symbols to work
around the IR symbol table limitation. Note: before D97446, Clang never emitted
symbols in the `llvm.compiler.used` list, so this change does not punish any
Clang emitted global object.

Without the patch, `ff_h264_cabac_tables` may be assigned to a non-external
partition and get internalized. Then we will get a linker error because the
`cabac.c` definition is not exposed.

Differential Revision: https://reviews.llvm.org/D97755
2021-03-03 16:22:30 -08:00